Process of drying lithocarpus densiflora rehd. (tanoak) wood with radio wave energy



United States Patent O1 ice U.S. Cl. 34-1 Claims ABSTRACT OF THEDISCLOSURE After harvesting and before seasoning degrade has occurreddue to nature or forced evaporation drying, tanoak wood is subjected toradio wave energy to effect a temperature of about 220 F throughout thetanoak wood. The subjection of the tanoak wood to radio wave energy iscontinued until about one third or more of the desired weight loss inthe wood is attained. While the moisture is being removed, the radiowave power is maintained at a level which prevents the temperature ofthe moisture contained in the tanoak wood from exceeding about 220 F.After about one third of the desired weight loss in the tanoak wood isattained by radio Wave energy, it may be dried further either bystandard non-radio wave evaporative drying techniques or by continuingto subject the tanoak wood to radio wave energy.

BACKGROUND OF THE INVENTION Lithocarpus densiflora Rehd. (Tanoak) Wood,hereinafter referred to as tanoak, is biologically classified as ahardwood. It has a finer grain structure than most other hardwoods, andthus does not split, flake and peel as much in use. Because of itsexcellent resilience characteristics, it has been found to beparticularly suited for making baseball bats. The hardwoodcharacteristics of tanoak wood also make it attractive for otherhardwood applications, such as, constructing hardwood floors, toolhandles, riot sticks, and furniture.

Unfortunately, tanoak wood cannot be economically dried by standardnon-radio wave evaporative drying techniques, such as, air drying, kilndrying, infrared drying and the like. Even though the great demand forhardwoods is depleting the stands of other hardwoods, tanoak wood stillhas been considered economically useless because it has been sodifficult and expensive to dry.

The principal problem encountered in drying tanoak wood by standardnon-radio wave evaporative drying techniques is tanoak woods tendency tosuffer irreversible seasoning degrade as a result of unequal shrinkageproduced in the wood as it is dried, Seasoning degrades common to tanoakwood are warping, checking, splitting, grain separation and cellcollapse. This seasoning degrade is detrimental to the quality of thetanoak wood produced and results in a very poor drying process yield ofuseful tanoak wood. This occurs even when tanoak wood is dried underconditions of carefully controlled humidity and temperature. Forexample, when tanoak wood is dried under such carefully controlledconditions, three to six months are required to complete the dryingprocess and the maximum process yield will be about fifty percent ofuseful tanoak wood with an average process yield of less than aboutthirty percent. The long time required to complete the drying processand the careful control of the humidity and temperature conditions.require a substantial investment in equipment and storage facilities.Even with such an investment, the average yield is so poor than tanoakwood has been too expensive for most uses of hardwoods. If tanoak woodis not 3,535,795 Patented Oct. 27, 1970 dried under such carefullycontrolled humidity and temperature conditions, excessive seasoningdegrade occurs. For the purpose of this application and in view of theabove discussions, seasoning degrade is considered excessive when theaverage process yields is less than about thirty percent of usefultanoak wood. For the foregoing reasons, both the lumber industry and US.Forest Service have classified tanoak wood as a weed.

Since seasoning degrade is irreversible, higher process yields can beobtained only by preventing damaging non-radio wave evaporative dyingafter the tanoak is harvested.

Drying wood with electromagnetic energy having a frequency in the radiowave range, i.e., about 10 kilohertz (kHZ.) to about 1000 gigahertz(gHz.) has been investigated for a number of years. Some of theseinvestigations have involved drying green soft and hard woodsexclusively with radio wave energy. Green wood is wood that has notsuifered seasoning degrade due to loss of moisture after being harvestedand before being subjected to a forced evaporative drying process.However, when compared to the costs of standard non-radio waveevaporative wood drying techniques, drying wood exclusively with radiowave energy has been economically impractical for large scale industrialapplications. Generally, drying wood exclusively with radio wave energyhas been economically impractical for two reasons. Firstly, radio waveenergy has been more expensive than that provided by other availableenergy sources for drying woods. To favorably compete with the otheravailable energy sources, drying with radio wave energy had to result inan enhanced quality product or yield produced in a much shorter time.Although in some cases the product quality, yield or production timehave been enhanced slightly when drying wood exclusively with radio waveenergy, it has not been enough to justify drying wood exclusively withradio wave energy in large scale industrial applications.

Another reason why it has been economically impractical to dry woodexclusively with radio wave energy is associated with the manner inwhich investigators have subjected the wood to radio wave energy. In anattempt to favorably compete with the other available energy sources, ithas been the practice to dry wood with radio wave energy as rapidly aspossible. This requires very high power levels which generally createextreme temperatures internally of the Wood causing the wood to bedamaged. Commonly this damage is in the form of rupture, shrinkage,internal cell collapse, and internal scorching.

In certain cases, it has been found economically practical to dry Woodwith radio wave energy techniques when combined with standardevaporative air drying techniques. In most of these cases, the wood isfirst subjected to air, generally, hot, to reduce its moisture contentfrom that of its green state to a level of about twenty percent byweight, dry basis and then subjecting it to radio wave energy to dry itto the desired final weight. In other cases, wood is subjectedsimultaneously to radio wave energy and hot air until the desired finalweight is achieved. When expressing moisture content percentages herein,it will be on the dry basis standard, determined by dividing the weightloss of the wood by the desired final weight of the wood and multiplyingby The desired final Weight of tanoak wood for optimum physicalcharacteristic has been determined experimentally and includes someresidual moisture content usually 6 to 10 percent by weight determinedby dividing the difference between the final desired weight and thefully dried weight of the wood by such fully dried weight andmultiplying However, in the case of green tanoak wood, it was found thatexcessive seasoning degrade will occur when drying it with air whethertanoak Wood is subjected to air drying in the presence or in the absenceof radio wave energy, and whether the air is cool or hot.

Considerable advantage is therefore to be gained by providing a processof drying tanoak wood which results in tanoak wood being an economicallyuseful hardwood. Additional advantages are to be gained by providing aprocess of drying tanoak wood which is economically practical for largescale industrial applications.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto render tanoak wood economically useful.

More specifically, it is an object of this invention to minimize thetendency of tanoak wood to suffer seasoning degrade caused by unequalshrinkage as it is dried.

Another object of this invention is to provide a high yield tanoak wooddrying process.

It is a further object of this invention to provide a process of dryingtanoak wood which is suitable for large scale industrial processing.

It is still another object of this invention to reduce the time requiredto dry tanoak wood without excessive seasoning degrade caused by unequalshrinkage.

It is yet a further object of this invention to dry tanoak woodeconomically with radio wave energy.

Yet another object of this invention is to dry tanoak wood with radiowave energy without forming destructive high temperature internally ofthe tanoak wood.

Still a further object of this invention is a. process for drying tanoakWood in which the tendency of the tanoak wood to check, split, suffergrain separation or warpage during drying is reduced.

The present invention is a process of drying tanoak wood with radio waveenergy, i.e., electromagnetic energy having a frequency in the range ofabout 1 megahertz to about 30 gigahertz. More particularly, it is aprocess of drying tanoak wood by subjecting it to radio wave energybefore non-radio wave evaporative drying effects excessive seasoningdegrade and thereafter continuing to subject the tanoak wood to radiowave energy at least until non-radio wave evaporative drying does noteffect excessive seasoning degrade.

In accordance with the process of the present invention, tanoak wood issubjected to radio wave energy at a power level suflicient to produce atemperature in the range of about 180 F. to 230 F. throughout the tanoakwood before non-radio wave evaporative drying effects excessiveseasoning degrade. If the temperature of the tanoak wood is less than180 F. at the commencement of subjecting it to radio wave energy somemoisture will be lost in increasing its temperature to the above range.The subjection of tanoak wood to'the radio wave energy is preferablycontinued until its moisture content is reduced by an amount at whichsubsequent non-radio wave evaporative drying does not effect excessiveseasoning degrade. As tanoak wood is dried, its moisture content is notmaintained uniform throughout its volume. Hence, the language moisturecontent refers to the average moisture content of the tanoak wood.

Tanoak wood can be dried exclusively with radio wave energy. However,drying with radio wave energy can be terminated prior to reaching thefinal desired moisture content level by weight-and non-radio waveevaporation drying employed to reduce the moisture content of the tanoakwood to its final desired level by weight without effecting excessiveseasoning degrade. Furthermore, if non-radio wave evaporative forceddrying techniques such as kiln drying, are employed to dry tanoak woodto its final moisture content level by weight rather than natural airdrying techniques and such drying is commenced before the tanoak woodcools substantially below the temperature it has at the termination ofsubjecting it to radio wave energy, it is not necessary to remove asmuch moisture from the tanoak wood with radio wave energy in order toavoid excessive seasoning degrade. Process yields of useful tanoak woodas high is ninety-five percent have been obtained by subjecting greentanoak wood to radio wave energy to effect a temperature in the range of180 F. to 230 F. throughout the tanoak and thereafter continuing tosubject it to radio wave energy until about /3 or more of the desiredweight loss in the tanoak wood is attained prior to placing the tanoakwood in kilns. Lesser process yields of useful tanoak wood are obtainedwhen less moisture is removed by radio wave energy prior to drying thetanoak wood in kilns.

If the tanoak wood is allowed to cool substantially after drying withradio wave energy (e.-g., to a temperature of less than 180 F.) beforeplacing it in a forced air dryer or subjecting it to natural air dryingtechniques to dry tanoak wood to its final moisture content level byweight, more moisture must be removed with radio wave energy to obtainthe same process yields of useful tanoak wood as in the case whereforced drying is commenced before the tanoak wood cools.

The yield of useful tanoak from the process of the present inventionvaries according to the amount of moisture removed from the tanoak woodby non-radio wave evaporative drying since seasoning degrade isirreversible, hence, cumulative. Thus, non-radio wave evaporative dryingbefore, simultaneously with and after drying with radio wave energy,must be controlled so that its cumulative effect does not produceexcessive seasoning degrade.

When subjecting tanoak wood to radio wave energy, the yield of theprocess is optimized by selecting the radio wave power level so that theinternal temperature of the tanoak wood is maintained below 230 F. atall times. If the internal temperature of the tanoak wood is allowed toexceed this level, damaging cell collapse, shrinkage, rupture and foodcharring are found to occur. To reduce these effects, the radio wavepower level is adjusted during drying to maintain the internaltemperature below about 230 F. and, preferably, not higher than about220 F.

By drying tanoak wood by the process of the present invention, excessiveseasoning degrade can be avoided and yields of useful tanoak wood atleast as high as ninety-five percent obtained. Although yields betweenthirty and fifty can be obtained by conventional nonradio waveevaporative drying techniques, greater expense and longer drying timesare required than in the cases where radio wave energy is used in dryingthe tanoak wood, e.g. four to six months as compared to one to sevendays.

The objects and advantages of the process of the present invention willbecome more apparent from the following detailed description of thepresent invention considered together with the appended claims.

DESCRIPTION OF PREFERRED PROCESS The process of the present inventionwill be described in detail as practiced to dry tanoak wood used formaking baseball bats. To obtain acceptable drying yields, at least abovethirty percent and preferably higher when drying tanoak wood to be usedin manufacturing baseball bats, prior to drying the harvested tanoaklogs or wood are kept under conditions which prevent the loss ofmoisture by non-radio wave evaporative drying sulficient to causeexcessive seasoning degrade. Moisture loss by nonradio wave evaporativedrying can be prevented various ways. For example, if the tanoak wood isnot dried shortly after harvesting, the tanoak logs could be placed inlog ponds until they are to be dried. Also, they could be stored in anenvironment having a relatively humid atmosphere of, for example, atleast sixty percent and, preferably, at a temperature not greater thanabout R, such as found in storage sheds. At a relative humidity of aboveeighty percent, the tanoak wood can be kept for several months withoutsuffering excessive seasoning degrade.

However, if the tanoak wood is subjected to radio wave energy shortlyafter harvesting, very little moisture 'will be lost through non-radiowave evaporative drying and excessive seasoning degrade will not occur.For example, if tanoak wood is allowed to stand in the atmosphere afterharvesting for about one week before subjecting it to radio wave energy,free moisture will be lost by gravity fiow and some moisture 'will belost due to evaporative air drying. The moisture loss that does occur asa result of evaporative air drying is slight and the tanoak :wood isstill considered to be in the green state. Yields greater thanninety-five percent have been obtained from tanoak wood which, afterharvesting and debarking, has been allowed to stand for one week in anatmosphere having a relative humidity of about sixty-five percent at atemperature of about 65 F.

Other techniques than those specifically described can be employedtoprevent moisture loss which results in excessive seasoning degrade.However, the specifically described techniques are convenient and makeuse of equipment and facilities presently employed in standard wooddrying processes.

Tanoak wood in various states of processing, such as logs, cut lumberand preshaped lumber, can be dried with radio Wave energy in accordancewith the method of the present invention. In manufacturing baseballbats, it has been found particularly advantageous to debark and cutgreen tanoak timber into billets having a cross sectional area of aboutsquare inches and a length of about 40 inches before subjecting them toradio wave energy, Furthermore, greater yields are obtained if sharpcorners are removed by preshaping the tanoak billets to have a crosssection in the plane of the growth rings defining a curved outline formsuch as circular or ovular. An additional advantage attendant topreshaping is that less radio wave energy is required to dry thepreshaped tanoak billet because the preshaped tanoak billet containsless total water.

Standard equipment employed in lumber mills can be used to cut and shapethe tanoak wood into the desired billets. For example, a tanoak log fromwhich billets are to be made might be passed through a debarker toremove the bark from the tanoak wood. After debarking the tanoak log,the tanoak wood would be passed through a saw, such as a circular saw,band saw, or log gang saw, to cut it into pieces having a crosssectional size that is desired for the billets. If the billets are to bepreshaped to have a circular or ovular cross section, the tanoak billetswould be passed through a contour cutting device, such as a lathe orshaper. After cutting the tanoak wood into pieces of the desired crosssectional size, they are passed through a trimmer to cut them intobillets of the desired I length of 40 inches.

The preshaped billets are then subjected to radio wave energy so thatexposure to non-radio wave evaporative drying does not result inexcessive seasoning degrade. The billets may be subjected to radio waveenergy in a continuous process or in a batch process. In a continuousprocess, the tanoak billets may be passed through a conveyorizedapplicator of radio wave energy, for example, at microwave frequencies,i.e., 1 mHz. to 30 gHz., a conveyorized cavity of the type described inthe British Pat. 1,043,290, published Sept. 21, 1966 by Morris R.Jeppson or in the U.S. application Ser. No. 675,172, filed Oct. 13, 1967by Jerome R. White and assigned to the assignee of this application, Atlower radio wave frequencies, conveyorized dielectric applicators wouldbe employed, such as described in the U.S. Pat. 2,868,939, issued Jan.13, 1959 by R. V. Pound. Preferably, the conveyorized radio waveapplicator would be positioned so as to receive the preshaped billetsdirectly from the trimmer via a linking conveyor means.

If the tanoak billets are to be exposed to radio wave energy in a batchprocess, they could be placed in a large closed cavity applicator, forexample, at microwave frequencies of the multimode microwave cavitytypes described in the U.S. Pat. 2,618,735, issued Nov. 18, 1952 to W.M. Hall or in the US application Ser No. 624,503, filed Mar 20, 1967 byRexford E. Black and assigned to the assignee of this application. Atlower frequencies, a dielectric heating applicator, for example, of thetype described in U.S. Pat. 2,783,344, issued Feb. 26, 1957 to H. R.Warren could be used. To dry the preshaped billets, they are removedfrom the trimmer and, to minimize nonradio wave evaporative drying,immediately placed in the radio wave applicator. The particular type ofradio wave applicator forms no part of the process of the presentinvention. Equivalent radio wave applications at those referred tohereinabove may be used with equal facility.

For large capacity operations, a number of billets are subjected at onetime to radio wave energy. In drying a large number of billets at onetime, for example, in a batch process by radio Wave energy at microwavefrequencies, they are placed in the multimode cavity in a configurationproviding spacing of at least about one inch between the sides ofadjacent billets. By placing the billets in such a configuration, a highdegree of uniform drying can be obtained.

The amount of microwave energy required to effect a temperature in therange of 180 .F. and 230 F. throughout the tanoak billets and to removea certain amount of moisture therefrom depends upon the number ofbillets being dried, the initial temperature of the billets, the size ofthe billets, and the initial moisture content of the billets. The energylevel is selected so that the billets Will not be damaged by highinternal temperatures created by subjecting the billets to too muchenergy. However, the energy must be sufficient to effect the desiredinternal temperature and remove the desired amount of moisture.

The level of power at which the tanoak billets are subjected tomicrowave energy determines the rate at which the temperature of thebillets reaches the range of 180 F. and 230 :F. and at which themoisture is removed from the billets. The rate is important because ifthe rate is too low, non-radio wave evaporative drying can becomesufficiently great to cause undesirable seasoning degrade, even to theextent of being excessive. If the power level is too high, the tanoakbillets shrink excessively and be come undesirably dense, and oftenrupture or suffer internal scorching. The power should be maintained ata level at which less than thirty percent shrinkage in diameter occurs.In the case of green tanoak billets having a size and shape as describedabove, it Was found that efficiency and yields are optimized if a billetis subjected to microwave power in the range of 0.3 kw. to 5 k w.

The above optimum power range is accurate for green tanoak billets ofthe above-described size and shape. For tanoak billets of differentsizes, shapes, and moisture content the optimum power range Wouldchange. However, the optimum power range easily can be determined fortanoak wood of any size and shape at various moisture content levels byexperimental methods. Such a method would be to expose various pieces oftanoak wood of a particular size, shape and moisture content todifferent levels of power and inspect the pieces for excessive shrinkage or seasoning degrade after the desired amount of moisture has beenremoved.

As described hereinbefore, drying tanoak wood in accordance with theprocess of the present invention can be conducted in various waysincluding exclusively with radio wave energy, with radio wave energycombined with forced evaporative drying and with radio wave energycombined with natural air drying.

In one case, tanoak wood billets were dried exclusively with radio waveenergy at microwave frequencies in a closed multimode microwave cavity.The tanoak bil lets were initially at room temperature, had a size andshape described hereinbefore and had an initial average green stateweight of eleven and one-half pounds and an average dry weight of fourand one-half pounds. The billets were placed in the microwave cavity ina configuration with a spacing of about one inch between the sides ofadjacent billets. Microwave power of 30 kw. at a frequency of 2450 mHz.was coupled into the cavity for about four hours to remove about fourand three-quarters pounds of moisture and, thereby, reduce the moisturecontent of the billets to about fifty percent, by weight. At thismoisture content level, the internal temperature of the tanoak woodbillets began to increase above 230 F. as additional moisture wasremoved at the input power level of 30 kw. If the input power level ismaintained at 30 kw. as the tanoak billets are dried below a moisturecontent of fifty percent by weight, the tanoak billets often rupture orsuffer internal scorching.

To minimize such damage to the billets, the power was decreased tomaintain the internal temperature of the billets below 230 F. as theaverage moisture content of the billets was reduced below fifty percentby weight. For example, as the average moisture content is reduced fromabout fifty percent to about forty percent by weight, the microwavepower level should be reduced to a maximum of about 1.125 kw. perbillet. This is accomplished by gradually reducing the microwave powerfrom 30 'klW. to about 22.5 klW. as the moisture content is reduced fromfifty percent to forty percent by weight. As the billets are furtherdried with microwave power to reduce their average moisture content toabout twenty percent by weight, the microwave power level should bereduced to a maximum of about 0.375 kw. per billet by gradually reducingthe power level to about 7.5 kw. At moisture content levels below fiftypercent, the reduction in the microwave power level is generally linearwith the reduction of the moisture content of the tanoak billets. Whendrying tanoak billets in this manner, a process yield of ninety-fivepercent was obtained and diameter shrinkage was maintained at about tenpercent.

The optimum power level for drying tanoak wood at various moisturecontent levels can be determined experimentally. One technique thatmight be employed would be to subject samples of tanoak wood havingvarious beginning moisture content levels of power for a definiteperiod. Immediately upon the termination of the application of thepower, the internal temperature of the samples would be measured byinserting a thermometer into the sample and the ending moisture contentdetermined by weight measurements as discussed above. The optimum powerlevels are those which produce an internal temperature in the range of212 to 230 F. By using this observed data as a guide in setting theradio wave power level for drying the tanoak wood, the tanoak wood canbe dried exclusively with radio wave power without subjecting it toexcesive levels of power. Thus process yields of useful tanoak billetsas high as ninety five percent may be obtained by drying green tanoakbillets exclusively with microwave energy in the manner described above.

Once the tanoak billets are dried to a moisture content of about fiftypercent by weight, they can be dried to their final moisture content byany of the non-radio wave evaporative drying techniques commonlyemployed in the lumber industry without causing excessive seasoningdegrade. For example, the tanoak billets could be removed from themicrowave applicator and placed in air for drying to the final desiredmoisture content by normal air drying.

Process yields of useful tanoak billets as high as ninety percent can beobtained by commencing microwave drying before the moisture content ofthe billets is reduced below about eighty five percent by weight bynon-radio [wave evaporative drying and, thereafter, continuing to drythe billets with microwave energy until their moisture content isreduced to about fifty percent by weight.

The process yield of useful tanoak billets depends upon the amount ofmoisture lost through non-radio wave evaporative drying beforecommencing, during, and after terminating radio wave drying. Forexample, if radio wave drying is started before non-radio waveevaporative drying reduces the moisture content of the tanoak billetsbelow about sixty percent and is continued at least until the moisturecontent is reduced to about fifty percent, excessive seasoning degradewill be avoided and process yields of at least thirty percent will berealized. Process yields of fifty percent will be obtained if radio wavedrying is commenced before the moisture content of the tanoak billets isreduced below about seventy percent by weight and continued at leastuntil the moisture content is reduced to about fifty percent. Althoughprocess yields between thirty and fifty percent can be realized byconventional non-radio evaporative drying techniques, much longer dryingtimes are required than when radio wave energy is used to dry tanoakwood, e.g., four to six months as compared to one to seven days.

With an exception to be discussed in detail hereinbelow, generally theprocess yield of useful tanoak billets will be less than optimum ifradio wave drying is terminated before the moisture content reachesfifty percent by weight. The amount of the decrease depends upon howmuch the moisture content of the tanoak wood is above fifty percent byweight when the radio wave drying is terminated.

If the tanoak billets are placed in kilns or other force type non-radioWave evaporative dryers after being subjected to radio wave energy, butbefore they cool substantially from the temperature they have at thetermination of being subjected to radio wave energy, the tanoak billetscan have much higher moisture content levels when subjected to non-radioevaporative drying without suffering seasoning degrade than in thosecases when they are allowed to cool before being placed in the kilns andthe like. In one case, green tanoak billets each of a size and shapedescribed hereinbefore are placed in a microwave oven and subjected to30 kw. of microwave power at frequency of 2450 mHz. until about threepounds of moisture are removed. The tanoak billets are then removed fromthe microwave cavity and placed in a kiln, preferably before thetemperature of the tanoak billets falls below F. and in a configurationto permit good circulation of air. The kiln is heated to a temperaturein the range of 212 F. to 220 F. To reduce the moisture content of thetanoak billets to the desired final moisture content by weight, theyremain in the kiln for about one week, the exact time depending upon theexact final moisture content desired as well as the volume of air flowand the temperature of the air directed through the kiln oven. Processyields of useful tanoak wood billets as high as ninety-five percent havebeen achieved by drying the billets in this manner.

Excessive seasoning degrade can be avoided, i.e., process yields greaterthan thirty percent can be obtained by subjecting green tanoak billetsto radio wave energy to raise their temperature throughout to the rangeof 180 F. to 230 F. and, after being brought to temperature, placingthem in a force type dryer, such as a kiln, to dry the billets to theirfinal desired moisture content. For example, eighty (80) green tanoakwood billets at room temperature and having a size, shape and moisturecontent as described hereinbefore were subjected to 30 kw. of microwavepower for about twenty minutes to raise their temperature to about 212F. The billets were then removed from the microwave applicator andplaced, for example, in a kiln before their temperature fell below about180 F. Drying the tanoak billets with radio wave energy and forced typedryers in the foregoing manner has the advantage of requiring less radiowave power than the other ways of conducting the process of the presentinvention but the average process yield may be lower.

It is possible to combine radio wave and air drying techniques to drythe tanoak billets after the tanoak wood no longer suffers excessiveseasoning degrade when exposed to non-radio wave evaporative drying. Insuch cases, a current of hot air at a temperature in the range of about210 F. to 220 F. would be established through the radio wave applicatorin contact with the tanoak billets. The hot air current serves to aid indrying the billets and exhausting the applicator.

However, when the tanoak billets are in a condition such that seasoningdegrade is caused when they are exposed to non-radio wave evaporativedrying, it is preferred to avoid establishing a current of hot airthrough the applicator for two reasons. Firstly, the hot air tends topromote undesirable non-radio wave evaporative drying. Secondly, the hotair current or even a cold air current, exhausts the moisture liberatedfrom the billets. It is desirable to keep the atmosphere in theapplicator humid during radio wave drying. The humid atmosphere keepsthe surface of the tanoak billets moist, thereby preventing theoccurrence of any significant surface evaporation. By confining at leastsome of the moisture removed from the tanoak billets in the applicatorso that a moist atmosphere having a relative humidity of at least aboutseventy (and preferably about eighty-five) percent surrounds the tanoakbillets, surface evaporation can be reduced and undesirable seasoningdegrade such as surface checking prevented.

In drying tanoak wood with radio wave energy, the radio wave energy canbe in the form of continuous wave power, pulse power or modulated power.The use of pulse or modulated power would allow the use of radio waveenergy at higher absolute power levels than possible with continuouswave power. Furthermore, it is possible to conduct radio wave drying atintervals whereby radio wave drying is terminated for extended periods.If the radio wave drying is terminated while the tanoak wood is stillsusceptible to seasoning degrade when exposed to non-radio waveevaporative drying, steps such as described hereinbefore should be takento prevent moisture lost through non-radio wave evaporative drying sothat the process yield is not reduced by the interruption of the radioWave drying.

By the process of the present invention, tanoak wood can be processed sothat it is an economically useful hardwood which can compete with otherhardwoods for the various hardwood uses. Furthermore, it has been foundthat baseball bats manufactured from tanoak wood may be superior tothose manufactured from other woods, commonly ash and hickory. Two ofthe more significant superior characteristics of tanoak baseball batsare fine grain structure which appears to contribute to longer life anda resilience which appears to provide an ability to propell a baseballfarther than baseball bats made from other woods. It is believed thattanoak wood has a lesser tendency to split in use in comparison to theother hardwoods due to its fine grain structure. It is also believedthat tanoak baseball bats will propell a baseball a distance about threepercent farther than baseball bats of other woods because ofthe superiorresilience of tanoak wood.

While the process of the present invention has been described in detailwith reference to drying tanoak of a particular size and shape, it isnot intended to limit the invention. As explained hereinbefore, whencompared with standard non-radio wave evaporating drying, superioryields are obtained in a shorter time and with less equipment andfacility expense even when tanoak wood is allowed to dry to an averagemoisture content by weight of sixty percent by non-electromagneticevaporative drying or the radio wave drying terminated before itsmoisture content is reduced to fifty percent. Hence, the presentinvention is not to be limited except by the terms of the followingclaims.

What is claimed is:

1. A process of drying tanoak wood to a selected moisture content levelwhich tanoak wood is to be used for manufacturing baseball bats and thelike comprising preshaping the tanoak wood into an elongated billethaving a cross section in the plane of the growth rings defining acurved outline form, subjecting the preshaped tanoak wood billet toradio wave energy at a selected power before its moisture content isreduced by non-radio wave evaporating drying to less than about sixtypercent dry weight, adjusting the radio wave power to maintain theinternal temperature of the tanoak wood billet in the range of about 212F. to 230 F., and continuing to subject the tanoak wood billet to radiowave energy to evolve moisture therefrom at least until subsequentnon-radio wave evaporative does not effect excessive seasoning degrade.

2. The process according to claim 1 further comprising maintaining themoisture content of the tanoak wood after harvesting at a level aboveabout eighty-five percent dry weight until subjected to radio waveenergy.

3. The process according to claim 1 wherein said tanoak Wood billet issubjected to radio wave energy before its average moisture content isreduced by non-radio wave evaporative drying to less than abouteighty-five percent dry weight, and further comprising surrounding saidtanoak wood billet with a moist atmosphere at least while subjected toradio wave energy.

4. The process according to claim 3 wherein said tanoak wood billet issubjected to radio wave energy without interruption until its moisturecontent level is reduced to said selected level.

5. The process according to claim 3 further comprising subjecting saidtanoak wood billet to drying air to evolve moisture therefrom after itsmoisture content is reduced so that non-radio wave evaporative dryingdoes not effect excessive seasoning degrade.

References Cited UNITED STATES PATENTS 2,543,618 2/1951 Wood 34-12,567,983 9/1951 Wood 34-1 3,031,767 5/1962 Wood 34--1 WILLIAM E.WAYNER, Primary Examiner US. Cl. X.R.

